We propose to continue our investigation of the properties, modes of action and regulation of the three E. coli Elongation Factors, EF-Tu, EF-Ts and EF-G which function with the guanine nucleotides and the ribosome to effect protein chain growth. We will examine the following conceptually and operationally related issues as they relate to these protein and the reactions in which they participate: 1. Definition of Factor active sites through selective chemical modification. 2. Substrate specificity and the mechanism of GTP hydrolysis by factors. 3. Metal ion involvement in factor function. 4. Location of interactions between the factors and the ribosome. 5. Mapping of interactions between EF-Tu and aminoacyl-tRNAs. 6. 3-dimensional structure as deduced by tryptic cleavage. 7. Regulation of Factor Synthesis and degradation. 8. Isolation and comparative properties of Eukaryotic Factors.